Devices, systems and methods for the removal of particles, free oil (such as dispersed, finely divided oil droplets), and emulsified oil contaminants in aqueous fluids is in widespread use in all types of commercial and industrial facilities. Known devices include cartridge and bag filters either permanently installed or as a part of portable systems, conventional oil coalescing systems that require many stages, baffles, filters, and weirs to coalesce and then separate and accumulate the coalesced oil, membrane filtration systems that concentrate emulsified oils and particles in an aqueous fluid for disposal, centrifuges that separate oil and particles due to their different densities, and conventional oil skimmers that use the higher viscosity of oils to remove oils in aqueous fluid sumps or baths after the oil droplets begin to coalesce due to time and gravity. Known methods also include periodically pumping out the old fluid and pumping in new fluid, periodically filtering the contaminated fluid over a relatively short period of time with portable filtration equipment in a dialysis mode, and filtering the contaminated fluid in an in-line mode at the aqueous fluid process flow rates.
However, each of these known devices, systems and methods, has its drawbacks. For example, in-line cartridge and bag filters are subject to blinding by oil emulsions and contaminants and require high-pressure pumps and housings. Oil coalescing systems are relatively expensive and difficult to clean and usually require a relatively large dedicated floor space, and do not remove emulsified tramp oils.
Membrane filters are unreliable due to their sensitivity to fouling by various contaminants and damage by pH and temperature. Membrane filters remove coalesced oils by holding back the oil and allowing aqueous fluids to pass through the filter. This concentrates the emulsion on one side of the membrane. As the concentration of oil increases, the efficiency of the filtration system decreases (due to increased resistance across the membrane) and the membrane becomes increasingly susceptible to fouling.
Centrifugal separation systems involve rapidly spinning elements to create the necessary centrifugal force, which can present safety concerns, and are relatively expensive.
Periodic change-out of the coolant results in labor time and costs, machine downtime, coolant costs and disposal costs. Periodic dialysis filtration in which the fluid is pumped out, filtered (either by centrifugal or conventional filtration) and returned to the sump requires labor to move from sump to sump. Moreover, once the coolant is periodically changed or filtered, it begins accumulating unwanted contaminants such that the quality of the coolant continually degrades until the next periodic change-out or filtration.
Various attempts have been made to reduce fouling in membrane filters. These include using spinning discs near the surface of the membrane; however, these disks require relatively large amounts of energy and generate heat in the fluid. Moreover, membrane pore sizes are such that bacteria concentrate with the emulsion. The heat generated from the antifouling mechanisms tends to colonize bacteria and create offensive odors. Further, membrane filtration systems cannot be used to filter emulsified oil coolants for reuse because the membrane removes the desired oil-in-water emulsion which blinds (clogs or fouls) the membrane.
With respect to oil-in-water emulsions, these are liquid systems that are particularly difficult to filter. Such liquid systems include, for example, coolant systems having a (desired) oil droplet “surrounded” by coolant. That is, the oil-in-water forms a micelle-like liquid system with a desirable oil in the nucleus of the micelle with the coolant surrounding the oil nucleus. The “desirable” oil may be, for example, a particular lubricating oil. In such systems, tramp oils such as (other, undesirable) lubricating oils, hydraulic fluids and part coating oils (collectively contaminants) may be present in the coolant system. These contaminants adhere or attach to the outer liquid of the system. It is these contaminants that must be removed, without removing the desirable oils.
Oil skimmers are essentially a remediation strategy to remove unwanted oils after they have become a problem. Floating oils typically prevent the movement of oxygen and create an environment for the cultivation of anaerobic bacteria. Floating oils can also form dry floating patches of material that are not effectively picked up by conventional skimming techniques. Furthermore, oil skimmers do not remove emulsified tramp oils. The emulsified oils can also become food to cultivate bacteria as well as change the cooling and machining enhancement properties of the coolant.
Accordingly, there is a need for a filter system that is less susceptible to fouling and that can remove unwanted contaminants. Desirably, such a filter system is configured to allow contaminants to first pass over a used area of the filter prior to exposing the contaminants to unexposed areas of the filter. Most desirably, such a filter system increases the ability of oil and particulate contaminants to be removed without prematurely blinding the filter media. Such a system most desirably operates at low-pressure differentials to promote high efficiency and to eliminate the need for high-pressure pumps and additional structural elements to support these higher operating pressures. It is a further desire that the separated contaminants are collected in a way that permits easy removal.